In general, a typical cable for power distribution comprises one or more conductors in a cable core that is covered by layers of polymeric materials including a first semiconducting shield layer (also known as a conductor shield or a strand shield); an insulation layer, usually crosslinked polyethylene (XLPE) or ethylene propylene rubber (EPR); a second or outer semiconducting shield layer (also known as an insulation shield); a wire shield, e.g., a metallic tape layer; and a protective jacket. The second semiconducting shield layer can be either bonded to the insulation layer, or it can be strippable from the insulation layer, with most power cable applications using a second semiconducting shield layer that is strippable from the insulation layer.
The current technology for cables comprising a second semiconducting shield layer that is strippable from the insulation layer is illustrated by such publications as U.S. Pat. Nos. 4,286,023, 6,858,296 and 8,889,992; EP 0 420 271 A1 and EP 1 420 271 A1; and WO 2009/042364A1 and WO 2004/088674 A. These publications teach second semiconducting shield compositions that comprise an (1) ethylene vinyl acetate copolymer (EVA) with a vinyl acetate (VA) comonomer content of 33%; (2) an acrylonitrile-butadiene rubber (NBR); (3) carbon black; (4) hindered amine type antioxidants; and (5) an organic peroxide. Second semiconducting shields made from these compositions typically have a strip force of greater than (>) 15 pounds per one-half inch (lb/0.5″) over a commercially available insulation layer made from EPR.
There is a continuing interest in reducing the adhesion required to remove the second semiconducting shield layer from the insulation layer to improve the ease of cable installations.